Wanted - Simple microphone schematic slightly OT

[simon111]

I have been trying to find a circuit that will allow me to mix two XLR microphones (3Pin) to a single XLR (3pin) output.

I don't want it to have a preamp, (i/e no gain stages - as the output will be going into a mixing desk). Can I do this passviely without any problems? Or do I need some sort of zero gain buffer/isolated transformer Y connection . e.g. RG Keens design,  in it?

If so , has anyone any ideas of how to do this so it suits the microphines low impedances and not guitars?

Thanks
Simon111